The present invention relates to the field of remote plasma sources; more particularly, the present invention relates to the ignition of transformer coupled plasma (TCP) sources.
Transformer coupled plasmas are routinely used in a number of different applications including materials processing, production of activated gases, pollutant abatement and many others. In such devices, the magnetic core of the excitation transformer is placed in close proximity to, around or within a vacuum chamber. When the primary winding of this transformer is excited with radio frequency (RF), the electromagnetic fields induced around the core sustain a gas plasma discharge within the vacuum apparatus.
One of the main advantages of TCPs is that the power capacitively coupled into the plasma is minimized, resulting in a decrease in chamber wall damage through ion bombardment and, consequently, in extended lifetimes for the plasma chamber. However, this advantage poses a problem for plasma ignition since the capacitive fields are needed to start a plasma discharge.
One of the solutions to this problem has been the introduction of an auxiliary capacitive discharge used to generate enough free charges within the plasma chamber so that an inductively coupled plasma can be established. This additional capacitive discharge is usually driven by an external high voltage circuit.
According to one embodiment, an apparatus is described. The apparatus includes a vacuum chamber, an electrical transformer coupled to the vacuum chamber, and an ignition circuit. The electrical transformer induces an electromagnetic field within the vacuum chamber. The transformer includes a primary winding and a magnetic core. In addition, the transformer includes a secondary winding, to which the circuit used to ignite the vacuum chamber is coupled. The ignition circuit is used to ignite the vacuum chamber.